Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $211.76   13.217%   $239.7483   $239.75   $239.75   $239.70  
  Purchase #2 $212.96   3.143%   $219.6533   $219.65   $219.65   $219.70  
  Purchase #3 $106.63   7.232%   $114.3415   $114.34   $114.35   $114.30  
  Purchase #4 $204.76   5.694%   $216.419   $216.42   $216.40   $216.40  
  Purchase #5 $49.41   10.821%   $54.7567   $54.76   $54.75   $54.80  
  Purchase #6 $149.93   12.672%   $168.9291   $168.93   $168.95   $168.90  
  Purchase #7 $224.38   6.838%   $239.7231   $239.72   $239.70   $239.70  
  7 purchase totals = $1,159.83       $1,253.5710   $1,253.57   $1,253.55   $1,253.50